Can knuckle cracking lead to arthritis?

Claim: Over the years, renowned authorities--mothers, aunts and a mother-in-law--warned Dr. Donald Unger that knuckle cracking leads to arthritis of the fingers.

Reality: For 50 years, Unger, cracked the knuckles of his left hand a least twice a day, leaving his right hand as a control. "Thus, the knuckles on the left were cracked at least 36,500 times, while those on the right cracked rarely and spontaneously," he wrote in the journal Arthritis & Rheumatism in 1998.

His lifelong research project showed no arthritis in either hand and no apparent differences between the two hands, a finding that earned him the 2009 Ig Nobel Prize in Medicine, which is awarded to research projects that "first make you laugh, then make you think."

He concedes that a larger group would be necessary to confirm his findings but says the results call into question whether other parental beliefs, such as the importance of eating spinach, are also flawed. "Further investigation is likely warranted," he wrote.

"Blinding would only be possible if the investigator didn't know left from right," he wrote in a commentary in the journal. "This is not likely since studies indicate that only 31 percent of primary care physicians don't know left from right. (The figure is reportedly somewhat higher for most specialists.)"

(More than two decades after Swezey's study, his then-12-year-old co-author "continues to enjoy frequent knuckle cracking without manifestations or evidence of arthritis.)"

A slightly larger (and more rigorous) 1990 study by Detroit researchers found that habitual knuckle crackers were not at higher risk for arthritis. But they were more likely to have hand swelling and lower grip strength.

Reached in his office in Thousand Oaks, Calif., Unger, 83, is still a little puzzled by all the attention, which comes 11 years after his letter was published. As a past president of the American College of Allergy, Asthma and Immunology and the author of more than 40 research papers, he says "to become 'famous' for this stupidity seems very strange."

Yet Unger remains good-natured about his 15 minutes of fame. He has already decided what his follow-up act will be.